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Background: Elevated blood lead levels (BLLs) have been associated with lung cancer in occupational studies. To assess whether this relationship extends to the general population (with lower BLLs) and with full adjustment for smoking (given that lead is a tobacco constituent), we conducted analyses within the National Health and Nutrition Examination Survey (NHANES) II (1976-1980) and III (1988-1994) cycles.
Methods: We included 4,293 and 15,671 participants in NHANES II and III, respectively, aged ≥ 20 with BLL measurements and mortality follow-up through 2014. We fit multivariable Cox models adjusting for smoking and other potential confounders to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for BLL associated with mortality for lung cancer.
Results: We observed a suggestive association between BLLs and lung cancer mortality in both NHANES II (189 deaths; HR 1.8, 95% CI 0.7, 4.7 for BLL ≥20.0 µg/dl vs <10.0 µg/dl, P_trend =0.12) and NHANES III (363 deaths; HR 1.4, 95% CI 0.9, 2.0 for BLL ≥10.0 µg/dl vs <2.5 µg/dl, P_trend =0.08). These associations were stronger among women (NHANES II: HR 2.7, 95% CI 0.7, 10.0, P_trend =0.07; NHANES III: HR 2.7, 95% CI 1.2, 6.5, P_trend =0.03). After stratifying on smoking status, the NHANES II association for women was present among both current smokers (HR 1.3, 95% CI 0.6, 2.7 for 90^th vs 10^th BLL percentile) and never/former smokers (HR 2.1, 95% CI 0.7, 6.2 for 90^th vs 10^th BLL percentile). In NHANES III, however, the association for women was observed only among current smokers (HR 1.8, 95% CI 1.2, 2.7).
Conclusions: We observed a suggestive association between BLLs and lung cancer mortality among women. While residual confounding from tobacco use may explain the NHANES III finding, the NHANES II finding appears to be independent of smoking.